Integrated particle filter for MEMS device

ABSTRACT

A micro-electro-mechanical system (MEMS) transducer including an enclosure defining an interior space and having an acoustic port formed through at least one side of the enclosure. The transducer further including a compliant member positioned within the interior space and acoustically coupled to the acoustic port, the compliant member being configured to vibrate in response to an acoustic input. A back plate is further positioned within the interior space, the back plate being positioned along one side of the compliant member in a fixed position. A filter is positioned between the compliant member and the acoustic port, and the filter includes a plurality of axially oriented pathways and a plurality of laterally oriented pathways which are acoustically interconnected and dimensioned to prevent passage of a particle from the acoustic port to the compliant member.

FIELD

Embodiments of the invention relate to a micro-electro-mechanical system(MEMS) device having an integrated particle filter; and morespecifically, to a MEMS microphone having an integrated filter toprevent particle ingress.

BACKGROUND

In modern consumer electronics, audio capability is playing anincreasingly larger role as improvements in digital audio signalprocessing and audio content delivery continue to happen. There is arange of consumer electronics devices that are not dedicated orspecialized audio playback or pick-up devices, yet can benefit fromimproved audio performance. For instance, portable computing devicessuch as laptops, notebooks, and tablet computers are ubiquitous, as areportable communications devices such as smart phones. These devices,however, do not have sufficient space to house relatively largemicrophones or speakers. Thus, microphones and speakers sizes arebecoming more and more compact and decreasing in size. In addition, dueto the compact devices within which microphones and speakers areimplemented, they are often located close to the associated acousticinput or output ports of the device and therefore susceptible to failuredue to particle and water ingress.

SUMMARY

In one embodiment, the invention relates to a MEMS device, for example aMEMS microphone, having an integrated particle filter made up of anumber of material layers which form interconnected pathways dimensionedto trap particles therein. In addition, the MEMS microphone having theintegrated filter therein may be formed using batch processing MEMSoperations and entire wafer dicing and down stream processing is done asif it were a single wafer.

More specifically, in one embodiment, the invention is directed to amicro-electro-mechanical system (MEMS) transducer, such as a MEMSmicrophone assembly, having an integrated particle filter. The MEMStransducer may include an enclosure defining an interior space andhaving an acoustic port formed through at least one side of theenclosure. A compliant member configured to vibrate in response to anacoustic input may further be positioned within the interior space andacoustically coupled to the acoustic port. A back plate may bepositioned within the interior space along one side of the compliantmember in a fixed position. The MEMS transducer may further include afilter positioned between the compliant member and the acoustic port.The filter may include a plurality of axially oriented pathways and aplurality of laterally oriented pathways which are acousticallyinterconnected and dimensioned to prevent passage of a particle from theacoustic port to the compliant member. For example, the filter mayinclude a plurality of material layers and the plurality of axiallyoriented pathways may be holes extending through the plurality ofmaterial layers and the plurality of laterally oriented pathways may bespaces extending along, or otherwise between, the plurality of materiallayers. In some cases, at least one of the plurality of axially orientedpathways or the plurality of laterally oriented pathways has a greaterresistance to the passage of the particle than another at least one ofthe plurality of axially oriented pathways or the plurality of laterallyoriented pathways. In still further embodiments, the plurality ofaxially oriented pathways may include a first axially oriented pathwayand a second axially oriented pathway which is closer to the compliantmember than the first axially oriented pathway, and an opening to thesecond axially oriented pathway may be smaller than an opening to thefirst axially oriented pathway. Still further, the plurality of axiallyoriented pathways may include a first axially oriented pathway and asecond axially oriented pathway, and at least one of the plurality oflaterally oriented pathways is between the first axially orientedpathway and the second axially oriented pathway. The filter may includea first material layer and a second material layer, and at least one ofthe plurality of axially oriented pathways may be an opening through thefirst material layer and at least one of the plurality of laterallyoriented pathways is a channel between interfacing surfaces of the firstmaterial layer and the second material layer. In addition, the pluralityof axially oriented pathways and the plurality of laterally orientedpathways may be dimensioned to trap the particle within the filter. Insome cases, the plurality of axially oriented pathways and the pluralityof laterally oriented pathways form a vent pathway from the acousticport to a portion of the interior space acoustically coupled to a sideof the compliant member facing away from the acoustic port. In addition,a surface of the filter facing the acoustic port may include ahydrophobic coating. In still further embodiments, a surface of at leastone of the plurality of axially oriented pathways or at least one of theplurality of laterally oriented pathways comprises an anti-stictioncoating. In some cases, the compliant member, the back plate and thefilter are part of a MEMS microphone formed using a MEMS processingtechnique.

Another embodiment of the invention may include a MEMS microphoneassembly having a substrate through which an acoustic port is formed anda MEMS microphone coupled to the substrate. The MEMS microphone mayinclude a compliant member acoustically coupled to the acoustic port, aback plate positioned along one side of the compliant member in a fixedposition and a filter including a plurality of material layers thatdefine a plurality of acoustic pathways which are acousticallyinterconnected and dimensioned to prevent passage of a particle from theacoustic port to the compliant member. In some cases, the plurality ofmaterial layers are polysilicon layers and the plurality of pathwayscomprise holes or openings formed within or between the polysiliconlayers. In some embodiments, the plurality of material layers comprise afirst silicon layer and a second silicon layer, and the plurality ofpathways comprise a first opening formed within the first silicon layerand a second opening formed within the second silicon layer, and thefirst opening overlaps a portion of the second opening. In still furtherembodiments, the plurality of material layers include a stack up of afirst silicon layer and a second silicon layer, and at least one of theplurality of pathways has an opening formed within the first siliconlayer and another of the plurality of pathways is a channel formedbetween the first silicon layer and the second silicon layer. Theplurality of pathways may be arranged in alternating layers of axiallyoriented pathways and laterally oriented pathways between the compliantmember and the acoustic port. At least one of the plurality of pathwayscloser to the compliant member may be narrower than another at least oneof the plurality of pathways farther from the compliant member. In somecases, a vent port is formed through the filter, and the vent portacoustically couples the acoustic port to a back volume chambersurrounding the MEMS microphone.

Another embodiment of the invention includes a process for manufacturinga micro-electro-mechanical system (MEMS) microphone assembly includingproviding a substrate and forming a MEMS microphone on the substrate,the MEMS microphone having a compliant member, a back plate positionedalong one side of the compliant member and a filter comprising aplurality of pathways which are acoustically interconnected anddimensioned to prevent passage of a particle to the compliant member. Insome embodiments, forming the filter of the MEMS microphone may includethe operations of depositing a sacrificial layer on the substrate,etching the sacrificial layer, depositing a polysilicon layer on theetched sacrificial layer, removing the etched sacrificial layer to forma first layer of pathways from the polysilicon layer and forming asecond layer of pathways on the first layer of pathways.

The above summary does not include an exhaustive list of all aspects ofthe present invention. It is contemplated that the invention includesall systems and methods that can be practiced from all suitablecombinations of the various aspects summarized above, as well as thosedisclosed in the Detailed Description below and particularly pointed outin the claims filed with the application. Such combinations haveparticular advantages not specifically recited in the above summary.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments are illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and they mean at least one.

FIG. 1 is a schematic cross-section of one embodiment of a MEMS device.

FIG. 2A is a magnified view of a cross-section of one embodiment of afilter of a MEMS device.

FIG. 2B is a magnified view of the cross-section of the filter of FIG.2A.

FIG. 3 is a magnified view of another embodiment of a filter of a MEMSdevice.

FIG. 4 is a schematic cross-section of another embodiment of a MEMSdevice.

FIG. 5 illustrates one embodiment of a processing operation formanufacturing a microphone assembly.

FIG. 6 illustrates one embodiment of a further processing operation formanufacturing a microphone assembly.

FIG. 7 illustrates one embodiment of a further processing operation formanufacturing a microphone assembly.

FIG. 8 illustrates one embodiment of a further processing operation formanufacturing a microphone assembly.

FIG. 9 illustrates one embodiment of a further processing operation formanufacturing a microphone assembly.

FIG. 10 illustrates one embodiment of a further processing operation formanufacturing a microphone assembly.

FIG. 11 illustrates one embodiment of a further processing operation formanufacturing a microphone assembly.

FIG. 12 illustrates one embodiment of a further processing operation formanufacturing a microphone assembly.

FIG. 13 illustrates one embodiment of a further processing operation formanufacturing a microphone assembly.

FIG. 14 illustrates a block diagram of some of the constituentcomponents of an embodiment of an electronic device in which anembodiment of the invention may be implemented.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth.However, it is understood that embodiments of the invention may bepracticed without these specific details. In other instances, well-knowncircuits, structures and techniques have not been shown in detail inorder not to obscure the understanding of this description.

In the following description, reference is made to the accompanyingdrawings, which illustrate several embodiments of the present invention.It is understood that other embodiments may be utilized, and mechanicalcompositional, structural, electrical, and operational changes may bemade without departing from the spirit and scope of the presentdisclosure. The following detailed description is not to be taken in alimiting sense, and the scope of the embodiments of the presentinvention is defined only by the claims of the issued patent.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention.Spatially relative terms, such as “beneath”, “below”, “lower”, “above”,“upper”, and the like may be used herein for ease of description todescribe one element's or feature's relationship to another element(s)or feature(s) as illustrated in the figures. It will be understood thatthe spatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(e.g., rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein interpreted accordingly.

As used herein, the singular forms “a”, “an”, and “the” are intended toinclude the plural forms as well, unless the context indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising” specify the presence of stated features, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, steps, operations,elements, components, and/or groups thereof.

The terms “or” and “and/or” as used herein are to be interpreted asinclusive or meaning any one or any combination. Therefore, “A, B or C”or “A, B and/or C” mean “any of the following: A; B; C; A and B; A andC; B and C; A, B and C.” An exception to this definition will occur onlywhen a combination of elements, functions, steps or acts are in some wayinherently mutually exclusive.

FIG. 1 is a schematic cross-section of one embodiment of a MEMS device.In one embodiment, the MEMS device may be a MEMS transducer. Forexample, the MEMS device may be a MEMS microphone assembly 100. The MEMSmicrophone assembly 100 may be any type of microphone assembly or modulethat includes a microphone that can be used in an electronic device topick up sound and convert it to an electrical signal. In one embodiment,MEMS microphone assembly 100 includes an enclosure 102 within which amicrophone 104, such as a MEMS microphone, is positioned. Enclosure 102may include a top wall or top side 106, a bottom wall or bottom side 108and a side wall 110 connecting the top side 106 to the bottom side 108.The combination of the top side 106, bottom side 108 and side wall 110may define an enclosed volume, chamber, or space 112 which surroundsmicrophone 104 and other components of microphone assembly 100positioned within enclosure 102. In some embodiments, one or more of thetop side 106, bottom side 108 and/or side wall 110 may be integrallyformed with one another as a single unit. In other embodiments, one ofthe sides may be formed by a substrate having circuitry formed therein(e.g., a printed circuit board). For example, top side 106 and side wall110 may be one integrally formed structure, for example a lid or cover,that is mounted to a bottom side 108, which is formed by a substrate(e.g., a silicon substrate), to form the enclosed space within which thevarious components can be positioned.

Enclosure 102 may further include an acoustic port 116 that allows for asound from the environment surrounding enclosure 102 to be input tomicrophone 104 within enclosure 102. In FIG. 1, acoustic port 116 isshown formed within bottom side 108 of enclosure 102. Microphoneassembly 100 of FIG. 1 may therefore be considered, or referred toherein as, a “bottom port” microphone. In other embodiments, acousticport 116 may be formed within top side 106 of enclosure 102. In suchembodiments, microphone assembly 100 may be considered a “top port”microphone. In still further embodiments, acoustic port 116 may beformed through side wall 110.

Microphone 104 may be positioned within enclosure 102 as shown. Forexample, microphone 104 may be mounted to, or formed with, bottom side108 of enclosure 102. As previously discussed, bottom side 108 may be asubstrate having circuitry (e.g., a printed circuit board) andmicrophone 104, or any of its associated components, may be electricallyconnected to the circuitry. Microphone 104 could be a MEMS microphone aspreviously mentioned, which is integrally formed with the substrateusing MEMS processing techniques. In other embodiments, the MEMSmicrophone separately formed and then mounted to the substrate.Microphone 104 may include, among other features, a sound pick-upsurface 120, a back plate 122 and a filter 124 that are suspended withinenclosure 102 by support members 126, 128. Sound pick-up surface 120 maybe any type of member suitable for operation as a sound pick-up surfacefor a MEMS microphone. For example, sound pick-up surface 120 may be asilicon plate that operates as a microphone diaphragm, membrane orotherwise compliant member that can vibrate in response to an acousticinput (e.g., a sound wave entering acoustic port 116). Back plate 122may be positioned along a side of sound pick-up surface 120 and in afixed position with respect to sound pick-up surface 120. For example,back plate 122 may be between sound pick-up surface 120 and acousticport 116 (e.g., below the side of sound pick-up surface 120 facingacoustic port 116). In other embodiments, back plate 122 is betweensound pick-up surface 120 and top wall 106 of enclosure 102 (e.g., abovethe side of sound pick-up surface 120 facing top wall 106), or in somecases, could be part of top wall 106. In some embodiments, the soundpick-up surface 120 and the back plate 122 may be conductive (e.g., havean electrode coupled thereto) such that they form a variable capacitorin which the transduction principle is the capacitance change betweenfixed back plate 122 and the movable sound pick-up surface 120 caused bythe incoming wave of sound. Microphone circuitry (e.g., anapplication-specific integrated circuit (ASIC) 130) may then convert thechange in capacitance into a digital or analog output.

Filter 124 may be an integrated particle filter positioned between soundpick-up surface 120 and acoustic port 116. In other words, the soundpick-up surface 120, back plate 122 and filter 124 may be formed as asingle unit using MEMS processing techniques. Filter 124 is thereforeconsidered “integrated” in that it is formed with, and inseparable from,the remaining components (e.g., sound pick-up surface 120 and acousticport 116) of microphone 104 during a MEMS processing operation. In thisaspect, filter 124 is different from a filter which might be separatelymounted, or adhered to, the microphone and over an input port, after themicrophone is manufactured. For example, filter 124 may include a seriesof interconnected holes, openings, passages, pathways, or the like,which are formed within or between, silicon layers and allow for thepassage of an acoustic input (e.g., sound waves) to sound pick-upsurface 120 but prevent the passage of undesirable particles. Furtherdetails regarding the structure of filter 124 will be described inreference to FIG. 2A-2B and FIG. 3 and a MEMS process for forming filter124 will be described in reference to FIG. 5-FIG. 13.

It should further be understood that in the illustrated embodiment, thespace 112 formed by enclosure 102 can be considered a back volumechamber which is acoustically coupled to a first side 120A of soundpick-up surface 120. Microphone 104 may further include a front volumechamber 114 that is acoustically coupled to a second side 120B of soundpick-up surface 120. In some embodiments, the back volume chamber orspace 112 is a substantially sealed chamber that is acousticallyisolated from the surrounding ambient environment and the front volumechamber 114. The front volume chamber 114 may acoustically connect thesound pick-up surface 120 to acoustic port 116 such that an acousticinput (e.g., sound wave (S)) through acoustic port 116 can travel tosound pick-up surface 120.

In some embodiments, microphone assembly 100 may further include an ASIC130 as previously discussed. For example, ASIC 130 could be mounted tobottom wall 108 of enclosure 102 as shown. ASIC 130, however, may bemounted to other sides of enclosure 102 as desired (e.g., top side 106).ASIC 130 may be electrically connected to microphone 104 and circuitrywithin the bottom wall 108 (e.g., where bottom wall is a substrate) bywires (or other electrically conductive coupling means) and be used toconvert the change in capacitance of microphone 104 as previouslydiscussed, into a digital or analog microphone output.

Aspects of one exemplary embodiment of a filter will now be discussed inmore detail in reference to FIG. 2A-FIG. 2B. In particular, FIG. 2A andFIG. 2B are magnified views of a cross-section of one embodiment of afilter of a MEMS device. The filter may be filter 124 previouslydiscussed in reference to FIG. 1. In this aspect, filter 124 isintegrally formed with the other microphone components (e.g., soundpick-up surface 120 and back plate 122) and positioned over acousticport 116 within bottom side 108 of enclosure 102. From this view, it canbe seen that filter 124 is made up of a number of interconnectedpathways 202, 204 that allow for sound (S) to pass through filter 124 tothe sound pick-up surface 120 (see FIG. 1) while preventing the passageof one or more of a particle (P). The interconnected pathways 202, 204may have different orientations, sizes, shapes, dimensions, and/orarrangements that are designed to trap, prevent, or increase aresistance to, particle (P) so that it does not pass entirely throughfilter 124.

Representatively, as can be seen from FIG. 2A, in one embodiment,pathways 202 may be considered axially oriented pathways that cause thesound wave (S) and/or particle (P) to travel in a substantially axialdirection as illustrated by arrow 206 (e.g., a direction parallel to anaxis of acoustic port 116). Pathways 204, may in turn, be consideredlaterally oriented pathways which redirect the passage of the sound wave(S) and/or particle (P) in a substantially lateral direction asillustrated by arrow 208. Each of pathways 202 and pathways 204 areinterconnected such that they create a tortuous network of channels thatare easy for sound waves (S) to pass through but difficult for particle(P) to pass through. For example, as shown in FIG. 2A, in someembodiments, the axially oriented pathways 202 are arranged in rows226A, 226B, 226C and 226D, and the laterally oriented pathways 204 arearranged in rows 228A, 228B and 228C. Rows 226A-226D and rows 228A-228Cmay include any number of pathways necessary to provide a tortuouspathway for particle ingress. In addition, rows 226A-226D of axiallyoriented pathways 202 may be arranged in an alternating pattern with therows 228A-228C of laterally oriented pathways 204 such that any particle(P) traveling through filter 124 is continuously redirected through amulti-layered network of pathways, thus making it more difficult to passthrough filter 124.

The sizes, shapes, dimensions and/or arrangements of axially orientedpathways 202 and/or laterally oriented pathways 204 themselves may beselected to further prevent the passage and/or trap particle (P) withinfilter 124. Representatively, in some embodiments, the sizes, shapes,and/or dimensions of pathways 202 and 204 are selected to vary aresistance of the pathways to the passage of particle (P). For example,a size of an opening to one or more of pathways 202 and/or pathways 204and/or the size of the entire pathway, may be different so that theparticle (P) may initially pass through some pathways, but then gettrapped when it reaches others. Representatively, the sizes of theopenings to the pathways, or the pathways themselves, of filter 124 maydecrease or become narrower in a direction toward the compliant membranesuch that a particle may be able to enter the filter through the largeropenings or pathways near acoustic port 116, but then becomes trapped bythe smaller openings or pathways within filter 124. The sizes may beselected depending upon the size of particle the filter is intended totrap or otherwise prevent passage of. For example, the size of someopenings may be larger than the anticipated particle size, while thesize of other openings closer to the compliant member within the MEMSdevice may be smaller than the anticipated particle size such that theparticle cannot pass through them.

For example, as shown in FIG. 2B, in one embodiment, a size (e.g., width212) of an opening 210 of an axially oriented pathway 202A may bedifferent than a size (e.g., width 216) of an opening 214 to anotheraxially oriented pathway 202B. In addition, a size (e.g., width 220) ofan opening 218 of a laterally oriented pathway 204A may be differentthan a size (e.g., width 224) of another laterally oriented pathway204B. For example, the size (e.g., width 212) of opening 210 of axiallyoriented pathway 202A may be greater than a size (e.g., width 216) ofopening 214 to axially oriented pathway 202B, and the size (e.g., width220) of opening 218 of laterally oriented pathway 204A may be greaterthan a size (e.g., width 224) of laterally oriented pathway 204B. Inthis aspect, particle (P) entering filter 124 from acoustic port 116 maypass through opening 210 to the axially oriented pathway 202A and travelthrough opening 218 to the laterally oriented pathway 204B but thenstart meeting resistance at opening 214 to the next axially orientedpathway 202B and opening 222 to the next laterally oriented pathway204B, and eventually become trapped within laterally oriented pathway204B.

In addition, it should be understood that in some embodiments, the sizesof the axially oriented pathways 202 may vary with respect to thelaterally oriented pathways 204. For example, opening 210 to axiallyoriented pathway 202A may be greater than opening 218 to laterallyoriented pathway 204A and opening 222 to laterally oriented pathway204B.

In addition, in some embodiments, a width along an entire length of apathway may be the same as the corresponding opening to the pathway,therefore one pathway may also be referred to herein as having anarrower or wider passage way or channel for particle ingress thananother pathway. For example, axially oriented pathway 202A may beconsidered wider than axially oriented pathway 202B, laterally orientedpathway 204A may be considered wider than laterally oriented pathway204B and/or one or more of the axially oriented pathways 202A, 202B, maybe considered wider or narrower than another of the laterally orientedpathways 204A, 204B.

Other variations in the relative sizes, shapes, dimensions and/orarrangements of the axially oriented pathways 202 and laterally orientedpathways 204 which would cause a particle (P) to become trapped withinfilter 124 are also contemplated. For example, in some embodiments,axially oriented pathways 202 within one of rows 226A-226D may bearranged such that they overlap, or are laterally or axially offset,with respect to axially oriented pathways 202 within another one of rows226A-226D. For example, as can also be seen from FIG. 2B, an opening 230of the axially oriented pathway 202B in row 226B is laterally or axiallyoffset with respect to an opening 232 of the axially oriented pathway202C in row 226C. Said another way, an axis of opening 230 and the axisof opening 232 are not aligned. In addition, there is at least onelaterally oriented pathway 204 (e.g., row 228B) between each of theaxially oriented openings 230 and 232. In this aspect, a straightpathway from one axially oriented pathway or opening to another axiallyoriented pathway or opening is prevented, thus creating even moretortuous arrangements within the pathways and thereby further increasinga resistance of the filter to the passage of particles (P).

In some embodiments, this alternating arrangement of axially orientedpathways 202 and laterally oriented pathways 204 may be formed by astack up of material layers, with some of the layers forming the axiallyoriented pathways and some of the layers forming the laterally orientedpathways 204 in between. For example, row 226A may be a material layer(e.g., layer of silicon) through which more than one hole or opening 210is formed to create a number of axially oriented pathways 202 within row226A. Similarly, rows 226B-226D may be additional material layers havingadditional holes or openings which form the remaining axially orientedpathways 202 within rows 226B-226D. Each of these material layersforming rows 226A-226D may be stacked on top of each other and spacedapart using spacers 234A, 234B and 234C. The corresponding gaps orspaces between each of rows 226A-226D then form the rows 228A-228C oflaterally oriented pathways 204. In other words, laterally orientedpathways 204 may be formed by interfacing surfaces of the adjacent rows(e.g., interfacing surfaces 236, 238 of rows 226A, 226B, respectively).It is further contemplated, however, that in other embodiments, rows226A-226D including axially oriented pathways 202 could be stackeddirectly on top of one another (not spaced apart) and rows 228A-228C,including laterally oriented pathways 204, omitted. In this embodiment,the sizes and/or alignment of the axially oriented pathways between rowsis varied to create a network of tortuous pathways as previouslydiscussed. For example, the axially oriented pathways within one row maybe offset with respect to the axially oriented pathways within theimmediately adjacent rows, such as by making some smaller than others orif they are of the same size, misaligning the openings. Details withrespect to the stack up of material layers forming the axially orientedpathways 202 and laterally oriented pathways 204 will be discussed inmore detail in reference to FIG. 5-FIG. 13.

FIG. 3 is a magnified view of another embodiment of a filter of a MEMSdevice. In this embodiment, filter 124 is substantially similar tofilter 124 described in reference to FIG. 1 and FIG. 2A-2B, except inthis embodiment, the pathways 202 and/or 204 include one or morecoatings to further enhance a resistance to the passage of a particlethrough filter, and/or the passage of liquids. In particular, one ormore of pathways 202, 204 may include a surface coating 302 that helpsto trap particles within pathways 202, 204. Representatively, surfacecoating 302 may be an anti-stiction surface coating that is applied toat least one surface of pathways 202, 204. In some embodiments, surfacecoating 302 may be applied to any pathway surfaces that are within theinterior of filter 124 in order to maximize the trapping of particleswithin filter 124. Representative anti-stiction surface coatings mayinclude, but are not limited to, a self-assembled monolayer (SAM)coating including a fluorinated fatty acid, or a siloxane SAM coating.It should be understood, however, that these are only representativeexamples of anti-stiction coatings, and that any coating suitable forenhancing a resistance of a pathway to the passage of a particle may beused. In addition, surface coating 302 may be a conformal coating havinga same thickness along one or more of pathways 202, 204, or may havedifferent thicknesses among pathways 202, 204, as desired. For example,in some embodiments, the thickness of the surface coating 302 may benon-conformal so that the size of some pathways are smaller (ornarrower) than other pathways, thus further increasing a resistance ofthe pathways to particle passage. In still further embodiments, it isalso contemplated that the coating may be a coating that traps theparticle upon contact with only a single filter surface and does notrequire two filter surfaces to trap the particle. In other words, acoating that is the opposite of the anti-stiction coating, which allowsfor two surfaces having momentary contact with one another to trap theparticle, and then separate.

In addition, in some embodiments, a hydrophobic coating 304 may furtherbe applied to filter 124 to help prevent water ingress through pathways202 and/or 204. Representatively, hydrophobic coating 304 may be appliedto the exterior surface 306 of filter 124, which faces acoustic port116. In this aspect, water which passes through acoustic port 116 willbe repelled away from filter 124, and in turn, pathways 202, 204 withinfilter 124.

FIG. 4 is a schematic cross-section of another embodiment of a MEMSdevice. The MEMS device may, for example, be a microphone assembly 400that is substantially similar to microphone assembly 100 described inreference to FIG. 1. In particular, microphone assembly 400 may includean enclosure 102 having a MEMS microphone 104 positioned therein. Inthis embodiment, however, a leak or vent port 402 to back volume chamberor space 112 is formed through filter 124. Vent port 402 may allow forsound wave (S) to travel through filter 124 to back volume chamber orspace 112 to, for example, equalize a pressure between the first side120A and the second side 120B of sound pick-up surface 120 and reduce asensitivity of microphone 104. It can be seen from the magnifiedexpanded view of filter 124 that as sound (S) travels through thepathways 202, 204, vent port 402 allows for leakage out of filter 124 tothe surrounding back volume chamber or space 112. Vent port 402 may haveany size and shape suitable to achieve venting or leakage of a desiredamount of sound to back volume chamber or space 112.

One representative process for manufacturing microphone assembly 100having integrated filter 124 will now be described in reference to FIG.5-FIG. 13. In particular, FIG. 5 illustrates an initial processingoperation 500 in which a sacrificial layer 504 is deposited on asubstrate 502. The substrate 502 may, for example, be a siliconsubstrate having, or within which, circuitry may be provided forelectrical connections. The sacrificial layer 504 may, for example, be asilicon dioxide layer that is deposited according to standard MEMSprocessing techniques.

FIG. 6 illustrates a further processing operation 600 in which thesacrificial layer 504 is etched to form a patterned sacrificial layer602. The patterned sacrificial layer 602 will form the axially orientedpathways within the filter once it is removed. Sacrificial layer 504 maybe selectively etched by photolithography and a wet etch or a dry etchaccording to standard MEMS processing techniques. Representativeetchants may include, but are not limited it, an acid (e.g.,hydrofluoric acid, buffered hydrofluoric acid, nitric acid basedetchants or the like), ionized gas or plasma.

FIG. 7 illustrates the further processing operation 700 of applying apolysilicon layer 702 to the patterned sacrificial layer 602. Thepolysilicon layer 702 may be planarized such that it is level with thetop of the sacrificial layer 602. Once the polysilicon layer 702 isapplied and planarized, a further etching operation 802 is performed toetch an opening 804 within substrate 502 as shown in processingoperation 800 of FIG. 8.

Opening 802 is then used to remove (such as by etching as illustrated byarrows 902) patterned sacrificial layer 602 leaving behind a first layerof pathways 904 (e.g., axial pathways 202 shown in row 226A of FIG. 2A)as shown in processing operation 900 of FIG. 9. Operations 500, 600,700, 800 and 900 may then be repeated as many times as necessary to forma stack up of axially and laterally oriented pathways within the filter(e.g., laterally oriented pathway 204 of row 228A and axially orientedpathways 202 of row 226B as discussed in FIG. 2A).

Representatively, an additional sacrificial layer 1002 (e.g., silicondioxide) may be applied to first layer of pathways 904 as shown inoperation 1000 of FIG. 10. Sacrificial layer 1002 may be etched aspreviously discussed to form a patterned sacrificial layer 1102, whichwill define the openings which form a second and third layer of pathwaysas shown in operation 1100 of FIG. 11. In this aspect, patternedsacrificial layer 1102 may be patterned so that any axial pathways oropenings will be offset with respect to the axially oriented pathways oropenings in first layer of pathways 904. In addition, the patternedsacrificial layer 1102 may be patterned to create spacers which willform a gap or spacing between axial pathways or openings, and in turn,the lateral pathways. Once patterned sacrificial layer 1102 is formed,polysilicon layer 1202 is formed around patterned sacrificial layer 1102in operation 1200 shown in FIG. 12. As shown in operation 1300 of FIG.13, patterned sacrificial layer 1102 is then removed (e.g., etched asshown by arrows 1302 using opening 804 of substrate 502) leaving behinda second layer of pathways 1202 stacked on top of first layer ofpathways 904. Second layer of pathways 1202 may include axially orientedpathways 202 and laterally oriented pathway 204, as previouslydiscussed.

Once the desired number of material layers and pathways are formed, theMEMS processing operations may continue to form the rest of themicrophone (e.g., sound pick-up surface 120 and back plate 122)according to any suitable MEMS processing techniques. In addition, itshould be understood that while FIG. 5-FIG. 13 show a single MEMS devicebeing formed, the operations disclosed herein may be part of a batchprocessing technique in which any number of additional MEMS devices arealso being produced simultaneously on a single substrate (e.g.,substrate 502). Once all of the MEMS devices are complete, they are thenseparated (e.g., using a dicing operation) into individual MEMS devicesfor integration within the desired electronic device. For example, theseparated MEMS devices may be MEMS microphones having an integratedfilter, which can then be mounted to a substrate of the device withinwhich it is to be implemented. In addition, it should be understood thatbecause the filter is integrally formed with the MEMS microphone duringMEMS processing, the filter is confined to the area of the MEMSmicrophone and has substantially the same footprint as the othercomponents of the MEMS microphone (e.g., sound pick-up surface and backplate). Thus, the resulting MEMS microphone achieves particle filtrationwithout increasing the overall size of the device package or requiringany additional manufacturing operations once MEMS processing iscomplete. Still further, as previously discussed, each of the layersused to form the filter and its interconnected pathways are made ofpolysilicon using MEMS processing operations, and are not intended toinclude any metal layers interspersed between the polysilicon layers orotherwise within of among the filter layers and/or pathways.

Turning now to FIG. 14, FIG. 14 illustrates a simplified schematic viewof one embodiment of an electronic device in which a microphone asdescribed herein may be implemented. For example, a portable electronicdevice is an example of a system that can include some or all of thecircuitry illustrated by electronic device 1400.

Electronic device 1400 can include, for example, power supply 1402,storage 1404, signal processor 1406, memory 1408, processor 1410,communication circuitry 1412, and input/output circuitry 1414. In someembodiments, electronic device 1400 can include more than one of eachcomponent of circuitry, but for the sake of simplicity, only one of eachis shown in FIG. 14. In addition, one skilled in the art wouldappreciate that the functionality of certain components can be combinedor omitted and that additional or less components, which are not shownin FIGS. 1-4, can be included in, for example, the portable device.

Power supply 1402 can provide power to the components of electronicdevice 1400. In some embodiments, power supply 1402 can be coupled to apower grid such as, for example, a wall outlet. In some embodiments,power supply 1402 can include one or more batteries for providing powerto an ear cup, headphone or other type of electronic device associatedwith the headphone. As another example, power supply 1402 can beconfigured to generate power from a natural source (e.g., solar powerusing solar cells).

Storage 1404 can include, for example, a hard-drive, flash memory,cache, ROM, and/or RAM. Additionally, storage 1404 can be local toand/or remote from electronic device 1400. For example, storage 1404 caninclude integrated storage medium, removable storage medium, storagespace on a remote server, wireless storage medium, or any combinationthereof. Furthermore, storage 1404 can store data such as, for example,system data, user profile data, and any other relevant data.

Signal processor 1406 can be, for example, a digital signal processor,used for real-time processing of digital signals that are converted fromanalog signals by, for example, input/output circuitry 1414. Afterprocessing of the digital signals has been completed, the digitalsignals could then be converted back into analog signals.

Memory 1408 can include any form of temporary memory such as RAM,buffers, and/or cache. Memory 1408 can also be used for storing dataused to operate electronic device applications (e.g., operation systeminstructions).

In addition to signal processor 1406, electronic device 1400 canadditionally contain general processor 1410. Processor 1410 can becapable of interpreting system instructions and processing data. Forexample, processor 1410 can be capable of executing instructions orprograms such as system applications, firmware applications, and/or anyother application. Additionally, processor 1410 has the capability toexecute instructions in order to communicate with any or all of thecomponents of electronic device 1400. For example, processor 1410 canexecute instructions stored in memory 1408 to enable or disable ANC.

Communications circuitry 1412 may be any suitable communicationscircuitry operative to initiate a communications request, connect to acommunications network, and/or to transmit communications data to one ormore servers or devices within the communications network. For example,communications circuitry 1412 may support one or more of Wi-Fi (e.g., a802.11 protocol), Bluetooth®, high frequency systems, infrared, GSM, GSMplus EDGE, CDMA, or any other communication protocol and/or anycombination thereof.

Input/output circuitry 1414 can convert (and encode/decode, ifnecessary) analog signals and other signals (e.g., physical contactinputs, physical movements, analog audio signals, etc.) into digitaldata. Input/output circuitry 1414 can also convert digital data into anyother type of signal. The digital data can be provided to and receivedfrom processor 1410, storage 1404, memory 1408, signal processor 1406,or any other component of electronic device 1400. Input/output circuitry1414 can be used to interface with any suitable input or output devices,such as, for example, microphone 104 of FIGS. 1-4. Furthermore,electronic device 1400 can include specialized input circuitryassociated with input devices such as, for example, one or moreproximity sensors, accelerometers, etc. Electronic device 1400 can alsoinclude specialized output circuitry associated with output devices suchas, for example, one or more speakers, earphones, etc.

Lastly, bus 1416 can provide a data transfer path for transferring datato, from, or between processor 1410, storage 1404, memory 1408,communications circuitry 1412, and any other component included in theelectronic device. Although bus 1416 is illustrated as a singlecomponent in FIG. 14, one skilled in the art would appreciate thatelectronic device 1400 may include one or more components.

While certain exemplary embodiments have been described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative of and not restrictive on the broad invention, andthat this invention is not limited to the specific constructions andarrangements shown and described, since various other modifications mayoccur to those of ordinary skill in the art. The description is thus tobe regarded as illustrative instead of limiting.

What is claimed is:
 1. A micro-electro-mechanical system (MEMS)transducer comprising: an enclosure defining an interior space andhaving an acoustic port formed through one side of the enclosure; acompliant member positioned within the interior space and acousticallycoupled to the acoustic port, the compliant member being configured tovibrate in response to an acoustic input; a back plate positioned withinthe interior space, the back plate being positioned along one side ofthe compliant member in a fixed position; and a filter positionedbetween the compliant member and the acoustic port, wherein the filtercomprises a plurality of material layers that define a plurality ofaxially oriented pathways and a plurality of laterally oriented pathwayswhich are acoustically interconnected, the plurality of axially orientedpathways extending through the plurality of material layers and theplurality of laterally oriented pathways extending between the pluralityof material layers, and a first axially oriented pathway of theplurality of axially oriented pathways is axially offset with respect toa second axially oriented pathway of the plurality of axially orientedpathways.
 2. The MEMS transducer of claim 1 wherein one pathway of theplurality of axially oriented pathways or the plurality of laterallyoriented pathways comprises a greater resistance to the passage of aparticle than another pathway of the plurality of axially orientedpathways or the plurality of laterally oriented pathways.
 3. The MEMStransducer of claim 1 wherein the second axially oriented pathway iscloser to the compliant member than the first axially oriented pathway,and wherein an opening to the second axially oriented pathway is smallerthan an opening to the first axially oriented pathway.
 4. The MEMStransducer of claim 1 wherein a laterally oriented pathway of theplurality of laterally oriented pathways is between the first axiallyoriented pathway and the second axially oriented pathway.
 5. The MEMStransducer of claim 1 wherein the plurality of material layers comprisesa first silicon material layer and a second silicon material layer, andthe first axially oriented pathways is an opening through the firstsilicon material layer and a laterally oriented pathway of the pluralityof laterally oriented pathways is a channel between interfacing surfacesof the first silicon material layer and the second silicon materiallayer.
 6. The MEMS transducer of claim 1 wherein the plurality ofaxially oriented pathways and the plurality of laterally orientedpathways are dimensioned to trap a particle within the filter.
 7. TheMEMS transducer of claim 1 wherein the plurality of axially orientedpathways and the plurality of laterally oriented pathways form a ventpathway from the acoustic port to a portion of the interior spaceacoustically coupled to a side of the compliant member facing away fromthe acoustic port.
 8. The MEMS transducer of claim 1 wherein a surfaceof the filter facing the acoustic port comprises a hydrophobic coating.9. The MEMS transducer of claim 1 wherein a surface of one of theplurality of material layers forming the first or second axiallyoriented pathways or a laterally oriented pathway of the plurality oflaterally oriented pathways comprises an anti-stiction coating.
 10. TheMEMS transducer of claim 1 wherein the compliant member, the back plateand the filter are part of a MEMS microphone formed using a MEMSprocessing technique.
 11. The MEMS transducer of claim 1 wherein thetransducer is a MEMS microphone assembly.
 12. A micro-electro-mechanicalsystem (MEMS) microphone assembly comprising: a substrate through whichan acoustic port is formed; and a MEMS microphone coupled to thesubstrate, the MEMS microphone having a compliant member acousticallycoupled to the acoustic port, a back plate positioned along one side ofthe compliant member in a fixed position and a filter, the filtercomprising a plurality of material layers defining a plurality ofpathways that are acoustically interconnected, wherein the plurality ofpathways comprise holes formed through each of the plurality of materiallayers and spaces separating each of the plurality of material layers.13. The MEMS microphone assembly of claim 12 wherein the plurality ofmaterial layers comprise polysilicon layers.
 14. The MEMS microphoneassembly of claim 12 wherein the plurality of material layers comprise afirst silicon layer and a second silicon layer, and the plurality ofpathways comprise a first hole formed within the first silicon layer anda second hole formed within the second silicon layer, and the first holeoverlaps a portion of the second hole.
 15. The MEMS microphone assemblyof claim 12 wherein the plurality of material layers comprise a stack upof a first silicon layer and a second silicon layer, and a first pathwayof the plurality of pathways comprises a hole formed within the firstsilicon layer and a second pathway of the plurality of pathwayscomprises a space formed between the first silicon layer and the secondsilicon layer.
 16. The MEMS microphone assembly of claim 12 wherein theplurality of pathways are arranged in alternating layers of axiallyoriented pathways and laterally oriented pathways between the compliantmember and the acoustic port.
 17. The MEMS microphone assembly of claim12 wherein a first pathway of the plurality of pathways closer to thecompliant member is narrower than a second pathway of the plurality ofpathways farther from the compliant member.
 18. The MEMS microphoneassembly of claim 12 wherein a vent port is formed through the filter,and wherein the vent port acoustically couples the acoustic port to aback volume chamber surrounding the MEMS microphone.
 19. A method ofmanufacturing a micro-electro-mechanical system (MEMS) microphoneassembly, the method comprising: providing a substrate; and forming aMEMS microphone on the substrate, the MEMS microphone having a compliantmember, a back plate positioned along one side of the compliant memberand a filter positioned along one side of the back plate or thecompliant member, the filter comprising a plurality of material layersthat form a plurality of pathways, wherein the plurality of pathways areacoustically interconnected and a pathway of the plurality of pathwaysis a laterally oriented pathway formed between at least two of theplurality of material layers.
 20. The method of manufacturing of claim19 wherein forming the filter of the MEMS microphone comprises:depositing a sacrificial layer on the substrate; etching the sacrificiallayer; depositing a polysilicon layer on the etched sacrificial layer;removing the etched sacrificial layer to form a first layer of pathwaysfrom the polysilicon layer; and forming a second pathway on the firstlayer of pathways.